The application of biacetyl as a reagent gas in chemical ionization (CI) mass spectrometry (MS) is being investigated. A preliminary study of several classes of compounds showed that biacetyl protonated all the compounds studied with non-bonding electrons or unsaturation. Unsaturated compounds also undergo the formation of an (M plus 43) species. Esters of cis and trans-4-t-butylcyclohexanol and endo and exo norbornane 2,3-diol were investigated using biacetyl as the reagent gas for CIMS. It was found that by careful control of source conditions, the less sterically blocked ester would undergo acetylation whereas the more sterically crowded ester would not.